Although recycling has a long history, it is only relatively recently that environmental protection and waste management issues have come to the forefront of both public and political awareness. Plastic recycling has predominately resulted from packaging applications such as packing films while other areas of polymeric waste include: construction, automotive, agriculture and electrical components.
Attempts at recycling cross-linked products have been attempted before, such as U.S. patent application Ser. No. 11/329,949 or U.S. Pat. No. 6,384,093, both of which are incorporated herein in entirety by reference. Both the '093 patent and the '949 application attempt to recycle cross-linked material through the addition of low molecular weight virgin resin through high-shear extrusion. When adding such low molecular weight species into a resin, properties can be significantly impacted, as low molecular weight species can lead to film weakness and tear propagation in the production of biaxially oriented films. Additionally, the '093 patent requires a dilution of up to 40 wt % of the recycled product with a virgin resin, further increasing the cost of the recycled product. U.S. Pat. No. 7,666,518, incorporated herein in entirety by reference, discloses a method to reprocess polyhydroxy amino ether-coated biaxially oriented polypropylene (BOPP) films using a compatibilizing agent of a functionalized polyolefin; using said reprocessed coated film back into new film; and having a low gel count. U.S. Pat. No. 5,286,424, incorporated herein in entirety by reference, discloses recycling polyolefin material, e.g. biaxially oriented polypropylene film, coated with a chlorine-containing polymer, such as polyvinylidene chloride homopolymer and/or copolymer, and having a primer therebetween by soaking the polyolefin material in a heated caustic solution until the material is separable from the chlorine-containing polymer. After separating the polyolefin material from the chlorine-containing polymer, the material is reprocessed into desired product by extrusion, molding or other product forming process.
In the production of BOPP films, the use of recycled or reprocessed propylene polymer-based pellets from waste or non-conforming BOPP films back into the core or base layer of said BOPP film is a common practice to reduce costs by replacing a portion of costlier virgin polypropylene material. Generally, the recycled material is similar in composition to the BOPP film it is being used in. This is to help maintain performance properties for the film's particular application and to maintain aesthetic appearance: It is generally desirable to have a film without gross defects such as gels, specks, excessive haze, low gloss, etc.
Some BOPP films can be modified with a skin layer to improve dramatically gas barrier properties. Such materials can either be coextruded or coated. In the case of coating, the skin layer can be applied via in-line coating (i.e. the barrier coating is done prior to transverse direction orientation in a sequential or simultaneous orientation line) or off-line coating (i.e. the barrier coating is done on a separate piece of equipment after the BOPP film is produced). Such high gas barrier materials are usually polar polymers like ethylene vinyl-alcohol (EVOH) or polyvinyl-alcohol (PVOH).
It is the objective of this invention to disclose a novel approach to allow for the re-introduction of crosslinked PVOH, EVOH, or blends thereof, into a cast, monoaxially oriented, or biaxially oriented polyolefin film.